The present invention relates to a light wave rangefinder for measuring a distance to an object of measurement by means of light reflected from the object of measurement without using a prism, and particularly to a light wave rangefinder that sends pointer light for visually recognizing a measuring area and position.
Recently, a light wave rangefinder 9000 has been developed which allows measurement of a distance to an object without using a prism or the like (hereinafter referred to as non-prism measurement). Light wave rangefinders that enable this non-prism measurement conventionally make distance measurement by receiving weak light reflected from an object, or obtain a distance by emitting pulse light having a high peak power and then measuring the time between emitting and receiving light to and from an object of measurement.
As shown in FIG. 9, a conventional light wave rangefinder 9000 is provided with a separate laser pointer 9900. The light wave rangefinder 9000 comprises a light emitting device 9100, a light emitting device driving unit 9110, a condenser lens 9120, a condenser lens 9130, a fiber 9140 on the light emitting side, a mirror 9150, an object lens 9160, a fiber 9170 on the light receiving side, a condenser lens 9180, a condenser lens 9190, a light receiving device 9200, an amplifier 9210, and a control arithmetic unit 9300. The separate laser pointer 9900 comprises a pointer light emitting device 9910, a pointer light emitting device driving unit 9920, and a pointer condenser lens 9930. Since a light receiving plane and a light emitting plane have a finite size, light rays a emitted from the object lens 9160 slightly spread out, and also an area b of light rays to be received, or an area from which light can be received, slightly widens for the same reason as the emitted light rays a side.
An area of non-prism measurement is a portion c where the emitted light rays a and the light rays b to be received overlap each other. When a light source providing a wavelength in an invisible range is used as the measuring light source 9200, the user cannot perceive the position being measured. Therefore, a laser pointer 9900 as described above is added for use as an auxiliary function.
However, in the case of a light wave rangefinder provided with the conventional laser pointer, an area of measurement and an area irradiated with the laser pointer do not coincide with each other, and therefore this presents a problem in that it is not possible to correctly grasp an area of measurement. This is because an area of non-prism measurement widens, as described above, while light rays d of the laser pointer are outputted as substantially collimated light rays. This means that an area of measurement visually perceived by the user by means of the laser pointer and an area where actual distance measurement is made do not coincide with each other. More specifically, the user can identify an approximate measuring location irradiated with the laser pointer on an object of measurement, but does not perceive the location c that is irradiated with measuring light rays and therefore contributes to distance measurement.
This presents a problem especially when distance measurement is to be made on a portion smaller than the area c of non-prism measurement. Even when the user collimates the laser pointer so that only a desired measuring location is irradiated, an area wider than the desired location is measured as a result. This tends to mislead the user, and will also result in a false distance value.
In order to avoid this problem, the area c of measurement and the area d irradiated with the laser pointer need to coincide with each other. However, in order to achieve this, it is required that the widening of the area of measurement and the spreading out of the laser pointer light coincide with each other and be disposed on the same axis, and furthermore, the directions of irradiation need to coincide with each other. Therefore, this presents a problem in that the cost of the mechanism and the cost of adjustment are greatly increased.
Next, there is a problem of degradation of a signal-to-noise ratio caused by laser pointer light entering a light receiving system of a distance measuring apparatus. In a conventional example in which an area c of non-prism measurement and the light rays d of a laser pointer are disposed on the same axis, the light of the laser pointer is reflected from an object of measurement and then enters a light receiving system of a distance measuring apparatus. As a result, light other than measuring light enters a light receiving device, thereby increasing shot noise in the light receiving device and degrading its signal-to-noise ratio. There is also a problem in that if the output of the laser pointer is increased in order to enhance the visibility of the laser pointer, degradation of the signal-to-noise ratio becomes even more noticeable.
The present invention is intended to provide a light wave rangefinder that sends pointer light for visually recognizing a measuring area and position. According to the present invention, there are provided a measuring light emitting device which emits measuring light rays; a light transmitting optical system which directs the measuring light rays at an object of measurement; a light receiving optical system which receives the measuring light rays reflected from the object of measurement; a light receiving device which receives the reflected measuring light rays and forms a light receiving signal; a control arithmetic unit which calculates a distance to the object of measurement on the basis of the light receiving signal; and a pointer light emitting device which introduces visible light into the light transmitting optical system.